This invention relates to a method for converting color picture signals regarding a picture image displayed on, for example, a screen of a color television set in which the picture image is reproduced with a highly purified color saturation and precisely in accordance with the changes of the brightness of colors, and a specified color can optionally be changed or modified, when it is required to obtain a hard copy of the picture image on the display unit such as color television set.
Recently, it has been necessary to obtain a hard copy of one scene of a picture displayed on a screen of a cathode ray tube (CRT) of a color television screen to reserve the scene for a long time. In that case, a hard copy is prepared by the color development of dyes of yellow (Y), magenta(M) and cyan(C) of color sensitive material on the basis of signals regarding blue(B), green(G) and red(R) colors of the television screen, respectively.
With one typical method of preparing such hard copy as described above, it has been proposed to firstly determine color development amounts of the yellow dye (Y) on the basis of the signal representing the blue color (B), of the magenta dye (M) based on the green color (G) signal, and of the cyan dye (C) based on the red color (R) signal. In this connection, the graph of FIG. 1 shows the color density with respect to signals inputted, and the graph shows condition of the density in a case where the signal representing the blue color is changed from the zero value (AA-point) to the maximum value (BB-point) with signals representing the green and red colors being maintained as the constant maximum values. The density characteristics Y1 of the yellow color on the basis of the blue color signal changes from the zero value to the maximum value (Dmax), and the density characteristics MC1 of the magenta and cyan colors on the basis of the green and red color signals always maintain the constant maximum value (Dmax). Spectral densities in such case as shown in FIG. 1 will be represented as shown in FIGS. 2A, 2B and 2C, in which FIG. 2A represents a condition at the AA-point shown in FIG. 1. FIG. 2B shows an ideal spectral density at the BB-point, but in actuality, the spectral density as shown in FIG. 2C will be obtained for the reason that the absorption of the blue color to the magenta (M) and cyan (C) dyes is not neglected, i.e. the subabsorption amount of the yellow color component is not zero. Accordingly, it is impossible to obtain a chromatic blue color such as shown on a color television screen.
In addition, a color reformation area of the photosensitive material is generally narrow in comparison with that on the screen of the color television set, so that the image of the color of the hard copy is not often matched with the color image of the television picture image. Moreover, in a conventional picture image outputting system, it is impossible to change or correct only the specified color for responding to the requirement for changing a color of a part of the obtained hard copy because of the unsatisfactory nature of the color of that part. For example, when the magenta color amount in the blue color is changed, the magenta dye, each with the same color amount as that in the blue color, in all colors related to the magenta color are adversely changed. Thus, a sufficient color adjustment cannot be attained in the conventional system for the aimed requirement.
Generally, since the color reappearing area of the photosensitive material is narrow in comparison with the color reappearing area of the screen of the color television set, a color image of the obtained hard copy is often not in accord with the picture image displayed on the television screen. Furthermore, in view of the produced hard copy, it is impossible for the conventional picture image outputting device or system to change or modify the specific color(s) with respect to a requirement for changing or modifying the color(s) of the specific portion(s). For example, even when it is necessary to modify the magenta dye amount in the blue color, the magenta dye amounts of all colors relating to the magenta are changed with the same amounts as that in the blue color, and accordingly, the color adjustment satisfying the aimed requirement cannot be achieved.